U.S. Pat. No. 4,524,550 discloses and claims an apparatus for removing flash from molded plastic and elastomeric articles and paint or coatings from various articles by contacting the articles with a blast media entrained in a cold carrier gas. The process operates by using the cold carrier gas, usually at cryogenic temperatures, to embrittle the flash or coating on the articles. The embrittled flash or coating being removed by the impact of the entrained solid particles which are in the form of shot, pellets, or irregular shaped particles. In one particular process, generally referred to a Cyrogenic Coating Removal (CCR) hangers used on a paint line in a manufacturing operation eventually become coated with many layers of paint which have to be removed. By placing these hangers in a device, such as shown in the '550 patent and having the hanger contacted by a particulate material (e.g., polycarbonate plastic) entrained in a nitrogen gas maintained at a temperature of -150.degree. F. to -225.degree. F. (-101.degree. C. to -143.degree. C.), the layers of paint can be embrittled and removed.
In the device of the '550 patent, the blasting particles, or blast media as they are sometimes called, and the coating or flash are collected in the bottom of the device, and removed from the device by a sweep for cleaning and recycling. The blast media is returned via a conveyor to a separator where it is separated from the flash or coating and collected in a storage hopper. The storage hopper, in turn, is connected via an auger or screw feed conveyor to the blasting apparatus or media blasting device for returning the blast media for reuse.
The problem with using an auger usually disposed at the bottom of the feed hopper, is that when the auger is stopped the blast media can and will settle into the screw conveyor, and when the screw conveyor is reactivated to restart the blasting cycle, the screw conveyor or augers, if there are more than one, will bind and will not drive.
At present, in order to avoid this problem, the operator of the device must keep the blast media level at a minimum while allowing full feed to the media throwing wheels in the blast or media treating chamber. This practice will tend to prevent overloading or binding of the augers or screw conveyor on restart after the media blasting device is turned off or the cycle interrupted.